a. Sure I do. It's pretty easy to reckon. I don't see "most" people traveling across the country and countries on a regular basis.
b. Sure, but again, that's a minority of even the professional demographic. Now, if you're thinking the developer demographic, sure I might agree with you, but that's not what OP said.
They don't need to travel across the country to need a laptop.
I have two data points for you:
The company I work for does little dev work. 99% of the people have laptops. They don't travel cross-country, mostly work in the office. But they also need to move to conference rooms, work from home, etc. We only have to handle one PC per person this way, instead of figuring how to handle their own personal PC when at home, etc. These are mostly "non IT people". Sure, you can argue they don't need the power of a desktop anyway. Which is absolutely correct.
I have a friend who does "actual dev work" working for an "actual software company". Java and C++, so they actually require powerful machines to compile (at least more than my company), etc. They used to have big-ass Xeon workstations. Those were replaced with some kind of Dell laptop [*] with a bunch of cores and RAM. He also basically never travels for work, but can now easily work from home without installing the company crap on his own PC. My friend is much happier with this arrangement.
Both companies provide multi-monitor setups with external keyboards and mice, so the comfort part of a desktop is still present when they're sitting at their desks.
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[0] They look like the XPS line, but seem somewhat thicker and don't have the XPS logo.
I wonder how energy prices are going to change that. If someone needs to pay $1000 a month to heat their homes all day in the winter because of WFH, I can see that tipping over lots of folks to go back to the office.
If that becomes an issue, I think it's reasonable that companies will start providing extra money to remote workers to cover operating costs. After all, those same companies will need to lease less office space (meaning lower costs for space and electricity).
b. Sure, but again, that's a minority of even the professional demographic. Now, if you're thinking the developer demographic, sure I might agree with you, but that's not what OP said.